[dpdk-dev] [PATCH] net/nfp: fix lock file usage
Alejandro Lucero
alejandro.lucero at netronome.com
Thu May 24 19:10:17 CEST 2018
On Thu, May 24, 2018 at 5:30 PM, Ferruh Yigit <ferruh.yigit at intel.com>
wrote:
> On 5/24/2018 4:39 PM, Alejandro Lucero wrote:
> >
> >
> > On Thu, May 24, 2018 at 3:15 PM, Ferruh Yigit <ferruh.yigit at intel.com
> > <mailto:ferruh.yigit at intel.com>> wrote:
> >
> > On 5/24/2018 3:13 PM, Ferruh Yigit wrote:
> > > On 5/24/2018 3:02 PM, Alejandro Lucero wrote:
> > >>
> > >>
> > >> On Thu, May 24, 2018 at 11:18 AM, Ferruh Yigit <
> ferruh.yigit at intel.com
> > <mailto:ferruh.yigit at intel.com>
> > >> <mailto:ferruh.yigit at intel.com <mailto:ferruh.yigit at intel.com>>>
> wrote:
> > >>
> > >> On 5/23/2018 5:50 PM, Alejandro Lucero wrote:
> > >> >
> > >> >
> > >> > On Wed, May 23, 2018 at 4:57 PM, Ferruh Yigit
> > <ferruh.yigit at intel.com <mailto:ferruh.yigit at intel.com>
> > <mailto:ferruh.yigit at intel.com <mailto:ferruh.yigit at intel.com>>
> > >> > <mailto:ferruh.yigit at intel.com <mailto:
> ferruh.yigit at intel.com>
> > <mailto:ferruh.yigit at intel.com <mailto:ferruh.yigit at intel.com>>>>
> wrote:
> > >> >
> > >> > On 5/23/2018 1:28 PM, Alejandro Lucero wrote:
> > >> > > DPDK apps can be executed as non-root users but
> current NFP lock
> > >> > > file for avoiding concurrent accesses to CPP
> interface is
> > precluding
> > >> > > this option or requires to modify system file
> permissions.
> > >> > >
> > >> > > When the NFP device is bound to VFIO, this driver
> does not
> > allow this
> > >> > > concurrent access, so the lock file is not required
> at all.
> > >> > >
> > >> > > OVS-DPDK as executed in RedHat distributions is the
> main NFP user
> > >> > > needing this fix.
> > >> > >
> > >> > > Fixes: c7e9729da6b5 ("net/nfp: support CPP")
> > >> > >
> > >> > > Signed-off-by: Alejandro Lucero
> > <alejandro.lucero at netronome.com <mailto:alejandro.lucero@
> netronome.com>
> > >> <mailto:alejandro.lucero at netronome.com
> > <mailto:alejandro.lucero at netronome.com>>
> > >> <mailto:alejandro.lucero at netronome.com
> > <mailto:alejandro.lucero at netronome.com>
> > <mailto:alejandro.lucero at netronome.com
> > <mailto:alejandro.lucero at netronome.com>>>>
> > >> >
> > >> > Hi Alejandro,
> > >> >
> > >> > As far as I understand this is to fix a common use case
> for
> > nfp, but it looks
> > >> > like there is already a workaround and only for
> non-root users.
> > >> >
> > >> >
> > >> > There is a patch submitted to stable versions because this
> lock was
> > also with
> > >> > the old NSPU interface, but as far as I know, there is no
> patch yet
> > for the
> > >> > current upstream tip.
> > >> >
> > >> >
> > >> >
> > >> > What is the priority of the patch, only critical but
> fixes
> > allowed at this
> > >> > point, can we push this one to next release?
> > >> >
> > >> >
> > >> > This is critical for us because RedHat wants to support OVS
> with
> > our card, and
> > >> > when OVS-DPDK is used, this problem is precluding non-root
> users to
> > execute
> > >> > OVS-DPDK.
> > >>
> > >> What exactly this lock for? Does it to prevent multiple
> primary
> > process to
> > >> access CPP interface?
> > >>
> > >> If so this is the know limitation in DPDK, not two separate
> process
> > can driver
> > >> same hardware, this is valid for all devices, why adding a
> lock
> > unique to nfp?
> > >>
> > >>
> > >> Time ago I had, by mistake, two different DPDK processes using
> same
> > device, and
> > >> with UIO, there is no one avoiding this.
> > >>
> > >> You can bound a device to UIO, igb_uio, and then use two
> different processes
> > >> opening the /dev/uiox file, and it works.
> > >
> > > But this is not anything specific to nfp, isn't it?
> >
> > Or let me ask something else, is this a fix for ovs-dpdk regular
> use-case with
> > nfp? Or this is just an extra protection in case multiple process
> may try to use
> > the NIC. If second, why it is critical?
> >
> >
> > I think any device bound to UIO could end up being used by two different
> DPDK
> > processes. So this is a protection against that possibility, because
> accessing
> > the NFP through the new CPP interface could make the NFP a brick even it
> could
> > crash the system.
>
> Yes and I was suggesting if we solve this, we should solve in higher level
> instead of PMD, but that is already in PMD this patch is not introducing
> it.
>
> >
> > RH is configuring OVS-DPDK for running as non-root, and the lock was
> precluding
> > this because it is set at /var/lock which a non-root user has not access
> by
> > default. This patch solves the problem, because when using the device
> with VFIO,
> > that lock is not necessary. And with UIO, the lock is needed and
> because it is
> > not possible to run DPDK apps with UIO as non-root, the lock path is
> fine.
>
> I see, this is to enable running as non-root by relaxing locking for vfio.
> OK,
> let me check the patch.
>
> But I still believe that locking shouldn't be in driver at fist place...
>
>
Agree. I think the UIO driver should be avoiding it, but not sure if there
are other reasons for not doing it.
> > >
> > >>
> > >> The VFIO driver does avoid this situation, but this lock is
> required for UIO.
> > >>
> > >
> >
> >
>
>
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